There were reports of two flying around last night as well, and so far, the police and Ministry of Defence have ruled it out as being theirs.

Bristows, which is based at Humberside Airport and holds the civilian search and rescue contract for the UK as well as flying offshore shuttles, said it wasn't one of their aircraft.

A spokesperson for the Coastguard and Maritime Agency has confirmed that the search and rescue helicopter is currently not out on a search and rescue mission but that it could be out in the area on training.

It has been identified as a Eurocopter Dauphin, a type used by Britain’s special forces.

The mystery further deepened as the flight did not appear on publicly available flight radars which track aircraft over UK skies, despite showing a number of airliners, private planes and other helicopters over Lincolnshire.

The Dauphin’s are operated by 658 Squadron of the Army Air Corps and are rarely seen.

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Painted in civilian colours they are designed to blend into normal civilian air traffic. Each can carry eight SAS soldiers and two were seen dropping off two teams of heavily armed special forces troops during the London terror attack earlier this month.

They can also be used to take troops speedily and nimbly into battle, dropping troops on top of rooftops.

An unmarked Dolphin helicopter, believed to belong to special forces, lands on London Bridge, following the terror attack on June 3 (Image: PA)

The squadron is based near the SAS HQ at Hereford.

The helicopter over Scunthorpe has caused a big debate on social media with people discussing different options.

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When asked by the Scunthorpe Telegraph if the helicopter was part of a special forces training operation, a spokesman for the Ministry of Defence said: "We don't comment on special forces."

An unmarked Dolphin helicopter, believed to belong to special forces, hovering next to London Bridge, following the terror attack on June 3 (Image: PA)

A military source told The Mirror: "These helicopters are extremely agile and quick - with the ability to get into smaller spaces, travel in-between high buildings with relative silence and at speed, with eight soldiers.

"They are ideal for tackling a dynamic situation like this and if needed could have been used to bring in extra forces , snipers or hostage rescue rescue teams."

Have you seen the helicopter out over Scunthorpe? Send us your pictures or footage in.